The present invention relates to recording systems and recording units employed in the recording systems for obtaining output images on recording paper that can meet a wide variety of needs in the printing industry in which high-speed output of high-quality images is required, in the printer industry oriented toward office and personal use requirements, and in the commercial equipment industry demanding inexpensive, general-purpose output devices which utilize versatile types of recording paper.
One known example of conventional color copying machines is a system shown in FIG. 16, which is based on color copying technology utilizing an electrophotographic process. According to this method, a DC-driven corona charger 102 uniformly places a positive electric charge by corona discharge on a surface of a photosensitive drum 101 in a case where the photosensitive drum 101 is formed of a p-type semiconductor, such as amorphous selenium or an amorphous selenium-tellurium alloy, for example. Then, a light beam produced by an exposure lamp 117 scans across a document glass plate 115, reflected light is passed through a filter 103 and a lens 104 to form an optical recording image in a color complementary to red, for example, and this optical recording image is projected onto the photosensitive drum 101 to form thereon an electrostatic latent image in the complementary color of red. This electrostatic latent image is developed into a visual image in red by a red toner developing unit 105.
Next, the electrostatic charge on the surface of the photosensitive drum 101 is eliminated by an AC-driven corona charge eliminating charger 113 and the photosensitive drum 101 is idled with a transfer charger 106, an AC-driven separation corona charger 107 and a cleaning blade unit 108 set in an OFF state. The DC-driven corona charger 102 places again a positive electric charge on the surface of the photosensitive drum 101, an electrostatic latent image is formed by an optical recording image in a color complementary to yellow, and a visual image in yellow is developed by a yellow toner developing unit 109. Lastly, an optical recording image in a color complementary to blue is projected and a blue toner developing unit 110 develops a visual image in blue in a similar way. At this point, the photosensitive drum 101 carries on its surface a full-color visual image composed of red, yellow and blue components. Subsequently, the transfer charger 106 causes the full-color image to be transferred onto a recording medium 111 such as recording paper and the AC-driven separation corona charger 107 peel the recording medium 111 off the photosensitive drum 101. The recording medium 111 thus separated is passed through a thermal fixing unit 112 to produce a permanently fixed image and delivered onto an output tray 116. On the other hand, the electrostatic charge on residual toner left on the surface of the photosensitive drum 101 is eliminated by the AC-driven corona charge eliminating charger 113, and the photosensitive drum 101 is cleaned by the cleaning blade unit 108. Further, residual charges left on the surface of the photosensitive drum 101 are removed by an erase lamp 114 in preparation for a succeeding color copying cycle.
Problems that have been encountered with the color copying technology based on the conventional electrophotographic approach are as follows:
(1) There are so many processing steps in the printing operation that it is difficult to reduce the physical size of a system.
(2) Since images in different colors are overlaid with one another on a single photosensitive drum, image misalignment and mixing of the different colors can occur.
Although copying machines based on ink-jet recording technology which can solve problem (1) of the aforementioned electrophotographic approach are available, the conventional ink-jet recording technology has been associated with the following problems:
(1) It is difficult to improve image resolution since a nozzle is used for spraying ink.
(2) The ink-jet recording technology can be divided into two types; these are continuous type and on-demand type. The continuous type provides a high recording speed, but system simplification is difficult due to the need for recovering unused ink. Contrarily, although system construction is simplified in the on-demand type, it is difficult to achieve a high recording speed.